Hydraulic transmission fluid



United States Patent amass HYDRAULIC TRANSMISSION FLUID William C.Howell, Jr., and Jones I. Wasson, Union, N. J., assignors to EssoResearch and Engineering Company, a corporation of Delaware 3. Claims.(Cl. 252-425) This application is a division of copending applicationSerial No. 306,500, filed August 26, 1952, now Patent No. 2,731,418.

The present invention relates to improvements in hydraulic transmissionfluids and more generally to lubricating compositions having superioranti-friction properties. The invention relates particularly to powertransmitting and lubricating compositions designed for use in hydraulictransmissions of modern automotive vehicles.

In the prior art numerous compositions have been proposed for use intorque converters, fluid clutches, semiautomatic and fully automaticautomotive transmissions and the like and in some cases difliculty hasbeen encountered in meeting certain specific requirements. This is notsurprising when it is considered that for many types of such automatictransmissions the fluid must act not only as a power transmission mediumbut in addition must provide satisfactory lubrication, act as ahydraulic control fluid, and perform as a heat transfer medium. Thefluid must also be free from corrosive eflects and objectionable odors.Moreover, the fluid must be so designed as to function properly over awide temperature range and it must possess a high level of oxidationresistance and a good degree of detergency. The latter properties areextremely important, since even small quantities of sludge and otheroxidation products, if allowed to settle out, can easily clog the verysmall orifices in the hydraulic control system and cause seriousmalfunctioning and damage to the transmission.

Although many of the numerous compositions of hydraulic transmissionfluids hereinbefore referred to have been satisfactory with regard tomost of the requirements as set forth above, to date no product has beenfound that is entirely satisfactory with respect to its anti-frictionproperties. In one popular type of torque converter transmission, forexample, under certain operating conditions there is sliding contactbetween certain elements and a tendency for them to alternately seizeand separate with stick-slip or chattering action. Ordinary lubricantssuch as straight mineral oil and a number of products especiallycompounded for the purpose do not prevent this objectionable type ofoperation. For example, the lubricants specifically recommended by themanufacturer of this transmission, known as Automatic TransmissionFluids, Type A, are completely inadequate for preventing this chatteringaction. This is true despite the fact that these approved fluids varywidely in their compositions and contain a wide variety of detergentinhibitor additives, anti-friction additives, and other materials.However, when the fluids described in this invention are used, theobjectionable chatter, particularly common when certain transmissionsare operated in reverse, is almost completely eliminated.

As has been previously mentioned, lubricants for use in automatichydraulic transmissions must, in addition to other important properties,possess a high degree of detergency, freedom from corrosion, and goododor. According to the present invention, it has been discovered2,768,953 Patented Oct. 30, 1956 ice that a particular combination ofdetergent inhibitors and acidic type materials, when combined in thecorrect proportions, give a fluid that has these desirable properties inoptimum combination. The specific acidic materials to be employed in agiven fluid depend upon the exact detergent-inhibitor used and thedetailed fluid properties desired. Oleic acid or similar unsaturatedlong chain fatty acids, or natural fats containing acids of this type(such as lard oil), may be used as anti-friction agents wheredetergent-inhibitors such as P2S5 treated barium salt of diisobutylphenol sulfide are employed.

Even better anti-friction properties can be obtained by the inclusion ofcertain phosphoric acid esters, especially triphosphate esters such astricresyl phosphate, along with the acid type anti-friction agent.Saturated long chain fatty acids such as stearic acid or alkyl mercaptoacids such as lauryl mercaptoacetic acid cannot be employed withdetergent-inhibitors of this type. By substituting an unsaturated acidsuch as oleic acid, or lard oil, H25 evolution is reduced, probably bybeing. taken up at the unsaturated bonds. When saturated acids areemployed, H28 evolution occurs, resulting in objectionable odor andcorrosion properties despite the fact that good anti-friction action isobtained. Also, substitution of a non-P285 treated detergent-inhibitorsuch as the barium salt of diisobutyl phenol sulfide for theP2S5-treated detergent material would reduce H2S evolution. However,such substitution cannot be made Without destroying the effectiveness ofthe anti-friction agent. Neither can detergent-inhibitors containingpetroleum sulfonates be employed for the same reason.

For improved anti-corrosion properties, combined withv better detergencyand better odor than is obtained with oleic acid-Pzss-treated detergenttype blends, it is preferred to use non-PzSs-treated detergentinhibitors. However, neither the saturated or unsaturated fatty acidsnor the mercapto acids are effective anti-friction agents in thepresence of these non-PzSs-treated detergent-inhibitors. It has beendiscovered, and is another feature of this invention, that if certainconcentrations of fatty acid and alkylmercapto acid are employedjointly, excellent antifriction properties result even in the presenceof the non-P2S5-treated detergent-inhibitors. Also, very good odor andcorrosion properties are observed for blends of this type because ofabsence of free H28. Sulfonatecontaining detergent-inhibitors cannot beused, however, without destroying the anti-friction properties.

The invention will be more fully understood by specific reference to aseries of blends which have been made in the study of the anti-frictionproblem. In general, two types of detergents were employed. One of thesewas a highly successful commercial product obtained by treating thebarium and/or calcium salt of diisobutyl phenol sulfide with aphosphorus sulfide such as P255. The other consists of the untreatedbarium or mixed bariumcalcium salt of diisobutyl phenol sulfide. Theformer gives superior anti-friction properties in combination with fattyacids but has an objectionable tendency to evolve HzS gas under certainconditions. The untreated salt, on the other hand, is free from .theobjectionable H28 evolution but is somewhat deficient alone or incombination with fatty acids, as an anti-friction agent in mineral baselubricating oil.

Byv combining certain concentrations of fatty acid of the C12 to C22range with a C8 to C24 alkyl mercapto acid, specifically lauryl mercaptoacetic acid, the combination is found to possess all the desiredproperties to an excellent degree. In the mercapto acids, instead oflauryl the alkyl group obviously may be octyl, Z-ethyl hexyl, decyl,tetradecyl, etc. Among the C12 to C22 fatty acids that may be used aremyristic, palmitic, stearic, erucic, brassidic, etc. In either case theaddition of a small Concen- Anti-Friction Agents tration, Detergcnt-Other Wt. Inhibitor Additives Percent Pour depres- Stcaric Acid 0. 3-0.4 sant, V. I. 1 Lauryl Mercapto Acetic Aei 0. 2-0. 3 A Improver,(Tricresyl Phosphate) 1 0. 5-1. 0 Anti-foam 01 A d 7 1 Agent eic ci 0. 0i (or No. 1 Lard on 2.0 i B May be omitted at the expense of a slightimpairment of antitriction properties.

A series of tests was made of various compositions in an actualhydraulic transmission of the torque converter type where a strongtendency to chatter was found in reverse gear operation. In theparticular transmission used, there is a large steel bearing surface inthe reverse planetary gear set which rotates against a bronze bushingwhen the unit is put into reverse. This bearing is lubricated by thetransmission fluid. As will be seen by reference to the data in Table I,when either straight mineral oil or the fluids presently approved by themanufacturer of this transmission are used, stick-slip occurs in thisbearing, and undesirable chatter is obtained. When the fluids describedin this invention are used, the chatter is almost entirely eliminated.

acetic acid. 10. 0.3% Stearic acid, 0.2% Lauryl mercapto acetic acid.11. No. 10+0.5% Tricresyl Very It. to Light.

Very Light. phosphate. 12. 0.4% Stearic acid, 0.5% 2.0% Detergent A.-.Medium to Heavy Trieresyl phosphate. 13. 0.3% Lauryl mercapto do Do.

acetic acid, 0.5% Tricresyl phosphate. 14. 0.2% Lauryl mercapto aceticacid, 0.3% Stearic acid. 16. 2.0% No. 1 Lard oil 2.0% Detergent A,

1.2% Calcium sulfonate concentrate.

2.0% Detergent 13...

Light to Medium.

Light.

1 Recommended by manufacturer for use in this transmission.

The concentration of the fattyacid and mercapto acid to be employed willdepend upon the nature of the other ingredients present and the requiredanti-friction prop erties. In general, the best concentration range forthe fatty acids is from about 0.2 to 1.0% by weight, and for themercapto acetic acid about 0.2 to 0.4%. Lower concentrations result indecreased efiectiveness while higher concentrations are objectionablefrom the standpoint of oxidation stability and corrosion. If tricresylphosphate 4 is also employed, a concentration of about 0.5% by weighthas been found to be efiective. Of those listed above in Table I,compositions Nos. 6, 10, 11 and 15 are most satisfactory over all.

In general, the invention contemplates the use of a lubricating oil as amajor component. This is preferably a mineral base lubricating oil,although synthetic oils such as dibasic acid esters, complex esters,polyglycols, and the like may be used so long as they are compatiblewith the additives. The preferred viscosity range is between 35 and S.S. U. at 210 F., particularly between 45 and 55 for the averagetransmission unit.

This lubricating oil base should contain about 1 to 6% by weight, basedon the total composition, of an alkaline earth metal salt of alkylphenol sulfide as a detergent, which is free from HzS evolution togetherwith 0.2 to 1% by weight of fatty acid of the C12 to C22 range, 0.2 to0.5 by weight of Cu to C18 alkyl mercapto acid, preferably an alkylmercapto acetic acid, and 0 to 1% by weight, preferably at least 0.2%,of a tri-ester of phosphoric acid, e. g. tricresyl phosphate, as anoiliness agent. When mineral oil is used as the fluid base it preferablyhas a viscosity between 35 and 65 S. S. U. at 210 F. and is ofreasonably high viscosity index. A preferred composition comprises 93.7to 97.4% of such a mineral base oil with 2 to 6% of the alkaline earthsalt of non-P285- treated alkyl phenol sulfide as detergent, 0.3 to 1%of a fatty acid, preferably a C18 acid, stearic acid being first choice,0.1 to 0.3% of lauryl mercapto acetic acid although other alkylderivatives may be used, and 0.2 to 1% of tri-cresyl phosphate.

It is to be noted that the invention as described contemplates the useof alkaline earth metal salts derived from the alkyl phenol sulfides asthe preferred detergents, and that the exact detergent-inhibitor to beemployed will depend upon the nature of the acidic type anti-frictionadditive to be used. It is also to be noted, however, that otherdetergent-inhibitors may also be used provided they do not interferewith the activity of the anti-friction agents employed or do not resultin objectionable corrosion or odor properties. Various other additivesmay also be included as required to impart specific properties to theblend such as conventional antioxidants, pour depressants, viscosityindex improvers, anti-foam agents, and the like.

What is claimed is:

1. A lubricant composition of high detergency and superior anti-frictionproperties, consisting essentially of a major proportion of alubricating oil of low viscosity, 1 to 6% by weight based on the totalcomposition of a P255 treated alkaline earth metal salt of alkyl phenolsulfide as a detergent, and 0.2 to 1% of oleic acid.

2. Composition according to claim 1 wherein a small amount of a triesterof phosphoric acid is added.

3. A composition having substantially the following components:

92 to 98.8% by weight of mineral lubricating oil base of 35 to 65 S. S.U. viscosity at 210 F.

1 to 6% P255 treated alkaline earth metal salt of diisobutyl phenolsulfide.

0.2 to 1% oleic acid 0.0 to 1% tricresyl phosphate.

References Cited in the file of this patent UNITED STATES PATENTS1,319,129 Wells Oct. 21, 1919 2,203,102 Powers June 4, 1940 2,237,336Caprio Apr. 8, 1941 2,451,345 McNab et al. Oct. 12, 1948

1. A LUBRICAN COMPOSITON OF HIGH DETERGENCY AND SUPERIOR ANTI-FRICTIONPROPERTIES, CONSISTING ESSENTIALLY OF A MAJOR PROPORTION OF ALUBRICATING OIL OF LOW VISCOSITY, 1 TO 6% BY WEIGHT BASED ON THE TOTALCOMPOSITION OF A P2S5 TREATED ALKALINE EARTH METAL SALT ALKYL PHENOLSULFIDE AS A DETERGEN, AND 0.2 TO 1% OF OLEIC ACID.